The present invention relates to an improvement in an excavator of the type wherein a center shaft is rotatably provided in a shield body in concentric relation to an outer cone, and an inner cone for crushing excavated materials in cooperation with the outer cone is eccentrically provided on the center shaft, and further a cutter head positioned in front of the inner cone is mounted on the center shaft. More particularly, the present invention relates to an excavator wherein a cutter head (crusher head) is provided with jet water spray nozzles, and jet water spray modes are switched between high-pressure spray and low-pressure spray according to the soil and obstruction conditions in an area to be excavated, and wherein jet water is mixed with an abrasive or an additive according to circumstances, and the rotational speed and torque of a cutter driving motor are also varied during excavation according to circumstances, thereby markedly improving shield and semi-shield machines in excavation function.
There have heretofore been known excavators, e.g. shield machines, in which a center shaft is rotatably provided in a shield body in concentric relation to an outer cone, and an inner cone for crushing excavated materials in cooperation with the outer cone is eccentrically provided on the center shaft, and further a cutter head having a plurality of roller cutters (roller bits) is mounted on a forward end portion of the center shaft in front of the inner cone. In this type of excavators, a motor with reduction gears is connected directly to the center shaft to rotate the center shaft, thereby rotating the cutter head. Alternatively, a motor with reduction gears and the center shaft are provided with respective externally-toothed gears, which are meshed with each other, to rotate the center shaft, thereby rotating the cutter head. The center shaft has a crankshaft shape in order to mount the inner cone eccentrically with respect to the outer cone. By the cooperation of the cutter head, the outer cone and the inner cone, materials to be excavated, i.e. earth and sand, gravel, and cobble stones, are continuously excavated.
Incidentally, soil conditions vary widely with working ranges, sites and depths. Even an excavation cross-section in one working area often contains an ordinary soil layer, a sandy soil layer, a gravel layer, a concrete layer, etc. in the form of an alternate layer structure. There may be a rock mass layer in addition to the above-mentioned layers. It is difficult to excavate ground having such soil conditions by using only one type of conventional excavator for reasons stated below.
(1) The optimum rotational speed and optimum torque of the cutter are different for different soil conditions. The cutter configuration also needs to be changed in conformity to each particular set of soil conditions.
(2) Regarding a system for conveying excavated materials, it is necessary to select a transport system according to soil conditions, e.g. a hydraulic transport system, a transport system using a screw conveyor, a transport system using a muck car, etc.
In the case of employing a hydraulic transport system, in particular, when gravel is transported as a crushed excavated material, the size of transportable gravel is determined by the diameter of a slurry discharge pipe used. Therefore, it is necessary to use an excavator capable of crushing gravel into pieces of a transportable size.
(3) When there are obstructions such as boulder gravel or a concrete layer, it is necessary to use a high-power excavator capable of previously tearing the obstructions and of crushing the boulder gravel into smaller pieces that can be taken into the excavator.
The relationship between the rotational speed and torque of the cutter for optimally excavating ground according to soil conditions is roughly as follows:
Ordinary soil, sandy soil medium speed, medium torque PA0 Sand gravel, gravel ground low speed, high torque PA0 Rock mass high speed, low torque
Because characteristics required for an excavator differ according to soil conditions and according to whether or not there are obstructions in layers to be excavated, as stated above, it has heretofore been all a single conventional excavator can do to excavate ground including only ordinary soil, sandy soil and a gravel layer, and necessary in order to excavate ground containing other large obstructions to use two or more different types of excavators.